Froth flotation is one of the most widely used process for beneficiating ores containing valuable minerals. It is especially useful for separating finely ground valuable minerals from their associated gangue or for separating valuable minerals from one another. The process is based on the affinity of suitably prepared mineral surfaces for air bubbles. In froth flotation, a froth or a foam is formed by introducing air into an agitated pulp of the finely ground ore in water containing a frothing or foaming agent. A main advantage of separation by froth flotation is that it is a relatively efficient operation at a substantially lower cost than many other processes.
It is common practice to include in the flotation process, one or more reagents called collectors or promoters that impart selective hydrophobicity to the valuable mineral that is to be separated from the other minerals. It has been suggested that the flotation separation of one mineral species from another depends upon the relative wettability of mineral surfaces by water. Many types of compounds have been suggested and used as collectors in froth flotation processes for the recovery of metal values. Examples of such types of collectors include the xanthates, xanthate esters, dithiophosphates, dithiocarbamates, trithiocarbonates, mercaptans and thionocarbonates. Xanthates and dithiophosphates have been employed extensively as sulfide collectors in froth flotation of base metal sulfide ores. One of the problems associated with these conventional sulfide collectors is that at pH's below 11.0, poor rejection of pyrite or pyrrhotite is obtained. In addition, as the pH decreases, the collecting power of the sulfide collectors also decreases rendering them unsuitable for flotation in mildly alkaline, neutral or acid environments. Suggestions have been made in the art for modifications of the xanthates and dithiocarbamates for improving their utility as sulfide collectors in a variety of froth flotation processes.
Dialkyldithiophosphoric acids and salts thereof such as the sodium, potassium, calcium or ammonium salts have been utilized as promoters or collectors in the beneficiation of mineral-bearing ores by flotation for many years. Early references to these compounds and their use as flotation promoters may be found in, for example, U.S. Pat. Nos. 1,593,232 and 2,038,400. Ammonium salt solutions of the dithiophosphoric acids are disclosed as useful in U.S. Pat. No. 2,206,284, and hydrollyzed compounds are disclosed as useful in U.S. Pat. No. 2,919,025.
The diesters of dithiophosphoric acids utilized as flotation promoters and collectors for sulfide and precious metal ores are obtained by reacting an alcohol with phosphorus and sulfur generally as P.sub.2 S.sub.5. The acid obtained in this manner can then be neutralized to form a salt which is stable yet soluble in water.
U.S. Pat. No. 3,086,653 describes aqueous solutions of alkali and alkaline earth metal salts of phosphoorganic compounds useful as promoters or collectors in froth flotation of sulfide ores. The phosphoorganic compounds are neutralized P.sub.2 S.sub.5 alkanol reaction products. Although single alcohols are normally used in the reaction, the patentees disclose that mixtures of isomers of the same alcohol, and mixtures of different alcohols may be utilized as starting materials in the preparation of the phosphorus compound, and the resulting acidic products can be readily neutralized to form stable solutions which are useful as flotation agents.
U.S. Pat. No. 3,570,772 describes the use of di(4,5-carbon branched primary alkyl) dithiophosphate promoters for the flotation of copper middlings. The 4 and 5 carbon alcohols used as starting materials may be either single alcohols or mixtures of alcohols.
Procedures for the selective flotation of copper from copper sulfide ores wherein a slurry of ore and water is prepared and sulfurous acid is added to the slurry to condition the slurry prior to the froth flotation step have been discussed in, for example, U.S. Pat. Nos. 4,283,017 and 4,460,459. Generally, the pulp is conditioned with sulfur dioxide as sulfurous acid under intense aeration. This conditioning of the slurry enhances the promotion and flotation rate of copper in the subsequent flotation step. Generally, the amount of sulfur dioxide added ranges from about 1 to 5 pounds of sulfur dioxide per ton of ore. In U.S. Pat. No. 4,283,017, the desirable pH of the conditioned slurry is reported to be between about 5 and about 6.5, and preferably between 5.5 and 6.0. In U.S. Pat. No. 4,460,459, the pH of the conditioned slurry is reported as being from about 6.5 to 6.8.